dtoc: Allow syncing of the device tree back to a file

At present we require the caller to manually update the device tree using
individual calls to libfdt functions. This is not ideal. It would be
better if we could make changes using the Python structure and then call a
Sync() function to write them back.

Add this feature to the Fdt class. Update binman and the tests to match.

Signed-off-by: Simon Glass <sjg@chromium.org>

tools/dtoc/test_fdt.py

@@ -337,6 +337,7 @@ class TestProp(unittest.TestCase):
         self.node.AddZeroProp('one')
         self.node.AddZeroProp('two')
         self.node.AddZeroProp('three')
+        self.dtb.Sync(auto_resize=True)
 
         # Updating existing properties should be OK, since the device-tree size
         # does not change
@@ -344,12 +345,17 @@ class TestProp(unittest.TestCase):
         self.node.SetInt('one', 1)
         self.node.SetInt('two', 2)
         self.node.SetInt('three', 3)
+        self.dtb.Sync(auto_resize=False)
 
         # This should fail since it would need to increase the device-tree size
+        self.node.AddZeroProp('four')
         with self.assertRaises(libfdt.FdtException) as e:
-            self.node.SetInt('four', 4)
+            self.dtb.Sync(auto_resize=False)
         self.assertIn('FDT_ERR_NOSPACE', str(e.exception))
 
+    def testAddNode(self):
+        self.fdt.pack()
+
 
 class TestFdtUtil(unittest.TestCase):
     """Tests for the fdt_util module